Multiple wavelength optical source

ABSTRACT

A planar optical waveguide is formed having sets of locking diffractive elements and means for routing optical signals. Lasers are positioned to launch signals into the planar waveguide that are successively incident on elements of the locking diffractive element sets, which route fractions of the signals back to the lasers as locking feedback signals. The routing means route between lasers and output port(s) portions of those fractions of signals transmitted by locking diffractive element sets. Locking diffractive element sets may be formed in channel waveguides formed in the planar waveguide, or in slab waveguide region(s) of the planar waveguide. Multiple routing means may comprise routing diffractive element sets formed in a slab waveguide region of the planar waveguide, or may comprise an arrayed waveguide grating formed in the planar waveguide. The apparatus may comprise a multiple-wavelength optical source.

RELATED APPLICATIONS

This application is a continuation of U.S. non-provisional applicationSer. No. 10/923,455 filed Aug. 21, 2004 (now U.S. Pat. No. 7,054,517),which in turn claims benefit of U.S. provisional App. No. 60/497,410filed Aug. 21, 2003, each of said provisional and non-provisionalapplications being hereby incorporated by reference as if fully setforth herein.

U.S. application Ser. No. 10/923,455 is also a continuation-in-part ofU.S. non-provisional application Ser. No. 10/653,876 filed Sep. 2, 2003(now U.S. Pat. No. 6,829,417), which is in turn a continuation-in-partof U.S. non-provisional application Ser. No. 10/229,444 filed Aug. 27,2002 (now U.S. Pat. No. 6,678,429), each of said non-provisionalapplications being hereby incorporated by reference as if fully setforth herein. U.S. application Ser. No. 10/229,444 in turn claimsbenefit of U.S. provisional App. No. 60/315,302 filed Aug. 27, 2001 andU.S. provisional App. No. 60/370,182 filed Apr. 4, 2002, each of saidprovisional applications being hereby incorporated by reference as iffully set forth herein.

U.S. application Ser. No. 10/923,455 is also a continuation-in-part ofU.S. non-provisional application Ser. No. 09/811,081 filed Mar. 16, 2001(now U.S. Pat. No. 6,879,441), and a continuation-in-part of U.S.non-provisional application Ser. No. 09/843,597 filed Apr. 26, 2001 (nowU.S. Pat. No. 6,965,464), application Ser. No. 09/843,597 in turn beinga continuation-in-part of said application Ser. No. 09/811,081. Saidapplication Ser. No. 09/811,081 in turn claims benefit of: 1) U.S.provisional App. No. 60/190,126 filed Mar. 16, 2000; 2) U.S. provisionalApp. No. 60/199,790 filed Apr. 26, 2000; 3) U.S. provisional App. No.60/235,330 filed Sep. 26, 2000; and 4) U.S. provisional App. No.60/247,231 filed Nov. 10, 2000. Each of said provisional andnon-provisional applications is hereby incorporated by reference as iffully set forth herein.

BACKGROUND

The field of the present invention relates to optical devicesincorporating distributed optical structures. In particular, a multiplewavelength optical source incorporating at least one distributed opticalstructure is disclosed herein.

Distributed optical structures employed in the multiple wavelengthoptical sources disclosed or claims herein may be implemented with avariety of adaptations, such as those described in:

U.S. non-provisional application Ser. No. 09/811,081 entitled“Holographic spectral filter” filed Mar. 16, 2001 in the name of ThomasW. Mossberg (now U.S. Pat. No. 6,879,441);

U.S. non-provisional application Ser. No. 09/843,597 entitled “Opticalprocessor” filed Apr. 26, 2001 (now U.S. Pat. No. 6,965,464);

U.S. non-provisional application Ser. No. 10/229,444 entitled “Amplitudeand phase control in distributed optical structures” filed Aug. 27, 2002in the names of Thomas W. Mossberg and Christoph M. Greiner (now U.S.Pat. No. 6,678,429);

U.S. non-provisional application Ser. No. 10/602,327 entitled“Holographic spectral filter” filed Jun. 23, 2003 in the name of ThomasW. Mossberg (now U.S. Pat. No. 6,859,318);

U.S. non-provisional application Ser. No. 10/653,876 entitled “Amplitudeand phase control in distributed optical structures” filed Sep. 2, 2003in the names of Thomas W. Mossberg and Christoph M. Greiner (now U.S.Pat. No. 6,829,417);

U.S. non-provisional application Ser. No. 10/740,194 entitled “Opticalmultiplexing device” filed Dec. 17, 2003 in the names of Dmitri Iazikov,Thomas W. Mossberg, and Christoph M. Greiner;

U.S. non-provisional application Ser. No. 10/794,634 entitled“Temperature-compensated planar waveguide optical apparatus” filed Mar.5, 2004 in the names of Dmitri Iazikov, Thomas W. Mossberg, andChristoph M. Greiner (now U.S. Pat. No. 6,985,656);

U.S. non-provisional application Ser. No. 10/798,089 entitled “Opticalstructures distributed among multiple optical waveguides” filed Mar. 10,2004 in the names of Christoph M. Greiner, Thomas W. Mossberg, andDmitri Iazikov (now U.S. Pat. No. 6,823,115);

U.S. non-provisional application Ser. No. 10/842,790 entitled “Multimodeplanar waveguide spectral filter” filed May 11, 2004 in the names ofThomas W. Mossberg, Christoph M. Greiner, and Dmitri Iazikov (now U.S.Pat. No. 6,987,911);

U.S. non-provisional application Ser. No. 10/857,987 entitled “Opticalwaveform recognition and/or generation and optical switching” filed May29, 2004 in the names of Lawrence D. Brice, Christoph M. Greiner, ThomasW. Mossberg, and Dmitri Iazikov (now U.S. Pat. No. 6,990,276); and

U.S. non-provisional application Ser. No. 10/898,527 entitled“Distributed optical structures with improved diffraction efficiencyand/or improves optical coupling” filed Jul. 22, 2004 in the names ofDmitri Iazikov, Christoph M. Greiner, and Thomas W. Mossberg.

Each of these applications and patents is hereby incorporated byreference as if fully set forth herein.

SUMMARY

A method for forming an optical apparatus comprises: forming a planaroptical waveguide; forming at least one set of locking diffractiveelements in or on the planar optical waveguide; forming means forrouting an optical signal corresponding to at least one said set oflocking diffractive elements; and positioning a laser corresponding toat least one said set of locking diffractive elements. The planaroptical waveguide substantially confines in at least one transversespatial dimension optical signals propagating therein. Each laser ispositioned so as to launch a corresponding laser optical signal into theplanar optical waveguide so that the corresponding laser optical signalis successively incident on the diffractive elements of thecorresponding locking diffractive element set. Each locking diffractiveelement set routes within the planar optical waveguide a fraction of thecorresponding laser optical signal back to the corresponding laser, witha corresponding locking transfer function, as a corresponding lockingoptical feedback signal, thereby substantially restricting thecorresponding laser optical signal to a corresponding laser operatingwavelength range determined at least in part by the correspondinglocking transfer function of the corresponding locking diffractiveelement set. Each corresponding routing means routes within the planaroptical waveguide, between the corresponding laser and a correspondingoutput optical port with a corresponding routing transfer function, atleast a portion of that fraction of the corresponding laser opticalsignal that is transmitted by the corresponding locking diffractiveelement set. The optical apparatus may comprise multiple lasers,multiple corresponding locking diffractive element sets, and multiplecorresponding routing means, thereby comprising a multiple-wavelengthoptical source.

The locking diffractive element sets may be formed in correspondingchannel waveguides formed in the planar optical waveguide, or may beformed in one or more slab waveguide regions of the planar opticalwaveguide. The multiple corresponding routing means may comprisecorresponding routing diffractive element sets formed in a slabwaveguide region of the planar optical waveguide, or may comprise anarrayed waveguide grating formed in the planar optical waveguide. Themultiple lasers may be individually assembled with the planar waveguide,may be assembled with the planar waveguide as an integrated laser array,or may be integrated directly into the planar waveguide. Thecorresponding laser output signals may be routed to a single output portor to multiple output ports.

Objects and advantages pertaining to diffractive element sets, planaroptical waveguides, or multiple-wavelength optical sources may becomeapparent upon referring to the disclosed embodiments as illustrated inthe drawings or disclosed in the following written description orappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and multiple routing diffractiveelement sets, and multiple lasers.

FIG. 2 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and multiple routing diffractiveelement sets, and multiple lasers.

FIG. 3 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and multiple routing diffractiveelement sets, and multiple lasers.

FIGS. 4A-4D are schematic cross-sections of diffractive elements in aplanar waveguide.

FIGS. 5A-5B are schematic top views of diffractive elements in a planarwaveguide.

FIGS. 6A-6B illustrate schematically termination of a channel waveguidecore in a planar waveguide.

FIG. 7 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and multiple routing diffractiveelement sets, multiple photodetectors, multiple variable opticalattenuators, and multiple lasers.

FIG. 8 is a schematic cross-section of diffractive elements in a planarwaveguide.

FIG. 9 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and multiple routing diffractiveelement sets, and multiple lasers.

FIG. 10 illustrates schematically a planar waveguide with multiplelocking diffractive element sets and an arrayed-waveguide grating, andmultiple lasers.

The embodiments shown in the Figures are exemplary, and should not beconstrued as limiting the scope of the present disclosure and/orappended claims.

DETAILED DESCRIPTION OF EMBODIMENTS

An optical apparatus according to the present disclosure comprises aplanar optical waveguide having at least one set of diffractiveelements. The planar optical waveguide substantially confines in atleast one transverse dimension optical signals propagating therein, andis generally formed on or from a substantially planar substrate of somesort. The confined optical signals typically propagate as transverseoptical modes supported or guided by the planar optical waveguide. Theseoptical modes are particular solutions of the electromagnetic fieldequations in the space occupied by the waveguide. The planar opticalwaveguide may comprise a slab waveguide, substantially confining in onetransverse dimension an optical signal propagating in two dimensionstherein, or may comprise a channel waveguide, substantially confining intwo transverse dimension an optical signal propagating therein. Itshould be noted that the term “planar waveguide” is not usedconsistently in the literature; for the purposes of the presentdisclosure and/or appended claims, the terms “planar optical waveguide”and “planar waveguide” are intended to encompass both slab and channeloptical waveguides.

The planar waveguide typically comprises a core surrounded bylower-index cladding (often referred to as upper and lower cladding, orfirst and second cladding; these may or may not comprise the samematerials). The core is fabricated using one or more dielectric,semiconductor, or other materials substantially transparent over adesired operating wavelength range. In some instances one or bothcladdings may be vacuum, air, or other ambient atmosphere. Moretypically, one or both claddings comprise material layers, with thecladding refractive indices n₁ and n₂ typically being smaller than thecore refractive index n_(core). (In some instances in which shortoptical paths are employed and some degree of optical loss can betolerated, the cladding indices might be larger than the core indexwhile still enabling the planar waveguide to support guided, albeitlossy, optical modes.) A planar waveguide may support one or moretransverse modes, depending on the dimensions and refractive indices ofthe core and cladding. A wide range of material types may be employedfor fabricating a planar waveguide, including but not limited toglasses, polymers, plastics, semiconductors, combinations thereof, orfunctional equivalents thereof. The planar waveguide may be secured to asubstrate, for facilitating manufacture, for mechanical support, or forother reasons. A planar waveguide typically supports or guides one ormore optical modes characterized by their respective amplitudevariations along the confined dimension.

The set of diffractive elements of the planar optical waveguide may alsobe referred to as: a set of holographic elements; a volume hologram; adistributed reflective element, distributed reflector, or distributedBragg reflector (DBR); a Bragg reflective grating (BRG); a holographicBragg reflector (HBR); a directional photonic-bandgap structure; amode-selective photonic crystal; or other equivalent terms of art. Eachdiffractive element of the set diffracts, reflects, scatters, orotherwise redirects a portion of an incident optical signal (saidprocess hereinafter simply referred to as diffraction). Each diffractiveelement of the set typically comprises some suitable alteration of theplanar waveguide (ridge, groove, index modulation, density modulation,and so on), and is spatially defined by a virtual one- ortwo-dimensional curvilinear diffractive element contour. The curvilinearshape of the contour may be configured to impart desired spatialcharacteristics onto the diffracted portion of the optical signal. Thecurvilinear contours may be smoothly curved, or may be approximated bymultiple short, substantially linear contour segments (in some instancesdictated by fabrication constraints). Implementation of a diffractiveelement with respect to its virtual contour may be achieved in a varietyof ways, including those disclosed in the references cited hereinabove.Each curvilinear diffractive element is shaped to direct or route itsdiffracted portion of the optical signal between input and outputoptical ports. The relative spatial arrangement (e.g. longitudinalspacing) of the diffractive elements of the set, and the relativeamplitude diffracted from each diffractive element of the set, yielddesired spectral or temporal characteristics for the overall diffractedoptical signal routed between the input and output optical ports. Itshould be noted that optical ports (input or output) may be definedstructurally (for example, by an aperture, waveguide, fiber, lens, laseror other optical source, or other optical component) or functionally(i.e., by a spatial location, size, convergence, divergence,collimation, or propagation direction), or both structurally andfunctionally. In some instances a pair of corresponding input and outputports may comprise the same optical port (i.e., the diffracted portionof the optical signal is retro-reflected). In some instances the inputand output ports may be interchanged (i.e., the action of thediffractive element set is symmetric). For a single-mode planarwaveguide, such a set of diffractive elements may be arranged to yieldan arbitrary spectral/temporal transfer function (i.e., diffractedamplitude and phase as functions of wavelength). In a multimode planarwaveguide, modal dispersion or mode-to-mode coupling of diffractedportions of the optical signal may limit the range of spectral/temporaltransfer functions that may be implemented.

The curvilinear diffractive elements of the set (or equivalently, theircorresponding contours) are spatially arranged with respect to oneanother so that the corresponding portions of the optical signaldiffracted by each element interfere with one another at the outputoptical port, so as to impart desired spectral or temporalcharacteristics onto the portion of the optical signal collectivelydiffracted from the set of diffractive elements and routed between theinput and output optical ports. The diffractive elements in the set arearranged so that an input optical signal, entering the planar waveguidethrough an input optical port, is successively incident on diffractiveelements of the set. For the purposes of the present disclosure orappended claims, “successively incident” shall denote a situationwherein a wavevector at a given point on the wavefront of an opticalsignal (i.e., a wavefront-normal vector) traces a path (i.e., a “raypath”) through the diffractive element set that successively intersectsthe virtual contours of diffractive elements of the set. Suchwavevectors at different points on the wavefront may intersect a givendiffractive element virtual contour at the same time or at differingtimes; in either case the optical signal is considered “successivelyincident” on the diffractive elements. A fraction of the incidentamplitude is diffracted by a diffractive element and the remainder istransmitted and incident on another diffractive element, and so onsuccessively through the set of diffractive elements. The diffractiveelements may therefore be regarded as spaced substantiallylongitudinally along the propagation direction of the incident opticalsignal, and a given spatial portion of the wavefront of such asuccessively incident optical signal therefore interacts with manydiffractive elements of the set. (In contrast, the diffractive elementsof a thin diffraction grating, e.g. the grating lines of a surfacegrating, may be regarded as spaced substantially transversely across thewavefront of a normally incident optical signal, and a given spatialportion of the wavefront of such a signal therefore interacts with onlyone or at most a few adjacent diffractive elements).

The set of diffractive elements provides dual functionality, spatiallyrouting an optical signal between an input optical port and an outputoptical port, while at the same time acting to impart aspectral/temporal transfer function onto the input optical signal toyield an output optical signal. The curvilinear diffractive elements maybe designed (by computer generation, for example) so as to provideoptimal routing, imaging, or focusing of the optical signal between aninput optical port and a desired output optical port, thus reducing orminimizing insertion loss. Simple curvilinear diffractive elements(segments of circles, ellipses, parabolas, hyperbolas, and so forth), ifnot optimal, may be employed as approximations of fully optimizedcontours. Numerous short, substantially linear segments may be employedto approximate a smoothly curved contour. A wide range of fabricationtechniques may be employed for forming the diffractive element set, andany suitable technique(s) may be employed while remaining within thescope of the present disclosure and/or appended claims. Particularattention is called to design and fabrication techniques disclosed inthe references cited hereinabove. The following are exemplary only, andare not intended to be exhaustive.

Diffractive elements may be formed lithographically on the surface of aplanar optical waveguide, or at one or both interfaces between core andcladding of a planar optical waveguide. Diffractive contours may beformed lithographically in the interior of the core layer or a claddinglayer of the planar optical waveguide using one or more spatiallithography steps performed after an initial deposition of layermaterial. Diffractive elements may be formed in the core or claddinglayers by projecting ultraviolet light or other suitable radiationthrough an amplitude or phase mask so as to create an interferencepattern within the planar waveguide (fabricated at least in part withsuitably sensitive material) whose fringe contours match the desireddiffractive element contours. Alteration of the refractive index byexposure to ultraviolet or other radiation results in index-modulateddiffractive elements. The mask may be zeroth-order-suppressed accordingto methods known in the art, including the arts associated withfabrication of fiber Bragg gratings. The amplitude or phase mask may beproduced lithographically via laser writer or e-beam, it may beinterferometrically formed, or it may be formed by any other suitabletechnique. In instances where resolution is insufficient to produce amask having required feature sizes, a larger scale mask may be producedand reduced to needed dimensions via photoreduction lithography, as in astepper, to produce a mask at the needed scale. Diffractive elements maybe formed by molding, stamping, impressing, embossing, or othermechanical processes. A phase mask may be stamped onto the core orcladding surface followed by optical exposure to create diffractiveelements throughout the core and or cladding region. The optical or UVsource used to write the diffractive elements in this case should have acoherence length comparable or longer than the distance from the stampedphase mask to the bottom of the core region. Stamping of the phase maskdirectly on the device may simplify alignment of diffractive elementswith ports or other device components, especially when those componentsmay be formed in the same or another stamping process. Many approachesto the creation of refractive index modulations or gratings are known inthe art and may be employed in the fabrication of diffractive elementsets.

Irradiation-produced refractive index modulations or variations forforming diffractive elements will optimally fall in a range betweenabout 10⁻⁴ and about 10⁻¹; however, refractive index modulations orvariations outside this range may be employed as well. Refractive indexmodulations or variations may be introduced by light of any wavelength(including ultraviolet light) that produces the desired refractive indexchanges, provided only that the photosensitive material employed issuitably stable in the presence of light in the desired operatingwavelength range of the optical device. Exposure of a complete set ofdiffractive elements to substantially spatially uniform,refractive-index-changing light may be employed to tune the operativewavelength range of the diffractive element set. Exposure of thediffractive element set to spatially non-uniform refractive-indexchanging light may be employed to chirp or otherwise wavelength-modulatethe diffractive element set (described further hereinbelow). Thesensitivity of planar waveguide materials to irradiation producedrefractive index modulations may be increased using hydrogen-loading,flame-brushing, boron or other chemical doping, or other method known inthe art, for example in the context of making fiber Bragg gratings.

The curvilinear shape of the diffractive element contours may bedetermined by a variety of standard optical imaging system design tools.Essentially, each diffractive element contour may be optimized to imagethe input port onto the output port in a phase coherent manner. Inputsto the design are the detailed structure of the input and output opticalports and their locations. Standard ray tracing approaches to opticalelement design may provide a diffractive contour at each opticaldistance into the planar waveguide that will provide an optimal imagingof the input signal at the input port onto the optimal output signal atthe output port. Simple curves may be employed as approximations of thefully optimized contours. Diffractive element virtual contours may bespaced by an optical path difference (as described above) that providesfor the field image of successive diffractive contours to besubstantially in phase at a desired wavelength. If the overall responseof the diffractive element set is to be apodized with amplitude or phasemodulation (to yield a desired spectral/temporal transfer function), theoptical spacing of successive diffractive element contours may be variedin a controlled manner to provide required phase differences betweendiffracted components at the output port, or the diffractive strength ofthe elements may be individually controlled (as disclosed in thereferences cited hereinabove).

An alternative approach to designing the diffractive element contoursfor a diffractive element set is to calculate interference patternsbetween numerically simulated fields at a desired wavelength and withspecified temporal waveforms entering the input port and exiting theoutput port. If a spectral transfer function is specified in a design, acorresponding temporal waveform may be obtained by Fourier transform. Informing or writing a summed pattern for the diffractive element set,suitable discretization is applied as needed for any lithographic or UVexposure approach that is utilized for fabrication. The holographicstructure may be designed by interference of computer-generated beamshaving the desired computer-generated temporal waveforms, with theresulting calculated arrangement of diffractive elements implemented bylithography or other suitable spatially-selective fabricationtechniques. For example, interference between a delta-function-likepulse and a desired reference optical waveform (or its time-reverse) maybe calculated, and the resulting interference pattern used to fabricatea diffractive element set that acts to either recognize or generate thedesired reference optical waveform.

In an alternative method for making the diffractive element structure,the core consists of a material of appropriate index that is alsophotosensitive at the wavelength of the desired operational signalbeams. As in traditional holography, the input and output recordingbeams (same wavelength as operational signal beams of the envisioneddevice) are overlapped in the core and the interference pattern betweenthem is recorded. Subsequently the core material is developed and, ifnecessary, a cladding may be deposited or attached by other means. Aspecified spectral transfer function may be generated by impartingspectrally sweeping the desired amplitude and phase variations on therecording beams, or the recording beams may be pulsed with temporalwaveforms having the desired Fourier spectrum.

The phrase “operationally acceptable” appears herein describing levelsof various performance parameters of planar waveguides and diffractiveelement sets thereof. Such parameters may include optical couplingcoefficient (equivalently, optical coupling efficiency), diffractionefficiency, undesirable optical mode coupling, optical loss, and so on.An operationally acceptable level may be determined by any relevant setor subset of applicable constraints or requirements arising from theperformance, fabrication, device yield, assembly, testing, availability,cost, supply, demand, or other factors surrounding the manufacture,deployment, or use of a particular assembled optical device. Such“operationally acceptable” levels of such parameters may therefor varywithin a given class of devices depending on such constraints orrequirements. For example, a lower optical coupling efficiency may be anacceptable trade-off for achieving lower device fabrication costs insome instances, while higher optical coupling may be required in otherinstances in spite of higher fabrication costs. In another example,higher optical loss (due to scattering, absorption, undesirable opticalcoupling, and so on) may be an acceptable trade-off for achieving lowerdevice fabrication cost or smaller device size in some instances, whilelower optical loss may be required in other instances in spite of higherfabrication costs and/or larger device size. Many other examples of suchtrade-offs may be imagined. Optical devices and fabrication methodstherefor as disclosed herein, and equivalents thereof, may therefore beimplemented within tolerances of varying precision depending on such“operationally acceptable” constraints or requirements. Phrases such as“substantially adiabatic”, “substantially spatial-mode-matched”, “so asto substantially avoid undesirable optical coupling”, and so on as usedherein shall be construed in light of this notion of “operationallyacceptable” performance.

Schematic plan views of exemplary embodiments of multiple-wavelengthoptical sources 1000 are shown in FIGS. 1-3. Multiple channel opticalwaveguide cores 1003 are formed in a region of planar waveguide 1001.Each channel waveguide core 1003 is positioned to receive acorresponding optical signal from a corresponding laser 1015. In FIG. 1,lasers 1015 comprise a set of individual lasers each independentlyassembled with the planar waveguide 1001. In FIG. 2, lasers 1015comprise an integrated laser array that is assembled with the planarwaveguide 1001. In FIG. 3, lasers 1015 are integrally formed on theplanar waveguide 1001. Drive current or electronic control signals maybe delivered to lasers 1015 via electrical conductors 1019. Eachcorresponding channel waveguide includes a set of locking diffractiveelements 1011. Each laser optical signal launched along thecorresponding channel waveguide core 1003 is successively incident onthe diffractive elements of the corresponding locking diffractiveelement set 1011. The locking diffractive element sets 1011 each routealong the corresponding channel waveguide core 1003 a fraction of thelaser optical signal launched by the corresponding laser 1015 into thechannel waveguide. The routed fraction of the optical signal is directedback to the laser to serve as a locking optical feedback signal. Eachlocking diffractive element set 1011 imparts onto the diffractedfraction of the optical signal a corresponding locking transferfunction, which determines at least in part the operating wavelengthrange of the corresponding laser 1015. The spectral characteristics ofthe locking transfer function are independent of the operating currentor other operating parameters of the laser, and the resulting opticalfeedback tends to substantially restrict the laser optical signal to aselected operating wavelength range in spite of variations in drivecurrent or other laser operating parameters.

The lasers 1015 may typically comprise semiconductor devices, whereininjection of drive current results in optical gain. The laser opticalsignals may be modulated by modulation of the laser drive currents. Thelaser may include two reflectors (e.g. opposing facets of asemiconductor laser chip) and thereby form a resonant optical cavity forsupporting laser oscillation. In this instance the combination of thelaser 1015 with the locking diffractive element set 1011 in the channelwaveguide results in an external-cavity feedback laser, wherein aportion of the laser output from the laser oscillator is re-injectedback through the output facet to stabilize the laser within thewavelength range determined by the locking diffractive element set. Inthis instance, compensation (active or passive) may be required so thatlongitudinal modes of the laser resonant cavity and the external cavitysubstantially coincide; otherwise, the laser output power or laserwavelength may fluctuate to an unacceptable degree as the respectivelongitudinal mode frequencies drift relative to one another.Alternatively, reflectivity of the front laser facet may be suppressed(by a suitable anti-reflection coating, for example, thereby diminishingor suppressing laser oscillation supported only within the laser chip),and the locking diffractive element set may serve as a laser resonatormirror. In this instance the laser 1015 and the channel waveguide withlocking diffractive element sets 1011 together comprise a hybridresonant optical cavity for supporting laser oscillation within thewavelength range determined by the locking diffractive element set. Bothof these scenarios shall fall within the scope of the present disclosureor appended claims.

The diffractive elements may be formed in the channel waveguides in anysuitable way, including but not limited to those listed hereinabove, andincluding but not limited to those disclosed in the incorporatedreferences listed hereinabove. Examples are shown in FIGS. 4A-4D, whichare schematic side cross-sectional views of diffractive elements in aplanar waveguide 11. The planar waveguide in these embodiments is formedon a substrate 9 and comprises a core 5 surrounded by cladding 1 and 3.Diffractive elements 8 may be formed within the core (FIG. 4A), in thecladding (FIG. 4B), on the cladding (FIG. 4C), at the interface betweencore and cladding (FIG. 4D), or any combination of these locations. Thediffractive elements 8 may comprise core material (FIG. 4B; FIG. 4D, ifthe diffractive elements protrude into the cladding as shown), claddingmaterial (FIGS. 4A and 4C; FIG. 4D, if the diffractive elements extendinto the core), or one or more materials differing from the corematerial and the cladding material (FIGS. 4A-4D).

The locking transfer functions may be determined by the particulararrangement of the elements of the corresponding locking diffractiveelement sets in each channel waveguide. A particular transfer functionis chosen to yield the desired spectral or temporal characteristics forthe optical feedback signal directed back to the laser, typically torestrict the laser optical signal to an operating wavelength range, orto otherwise optimize performance of the feedback-locked laser. Forexample, such a feedback-locked laser may exhibit reduced wavelengthfluctuations (within operationally acceptable limits) despite modulationof its drive current. The spectral locations λ₁, λ₂, λ₃, . . . λ_(N) ofthese operating wavelength ranges may be chosen in any desired fashion.In one example, operating wavelength ranges may be selected tosubstantially correspond to operating wavelength channels of awavelength-division-multiplexing (WDM) telecommunications system, suchas the ITU telecommunications grid. If the set of operating wavelengthsis spanned by the gain bandwidth of a single type of laser, then all oflasers 1015 may be substantially identical, with each operatingwavelength determined by the corresponding locking diffractive elementset.

To provide an optical feedback signal at a given vacuum wavelength λ, aperiodic spacing between the diffractive elements of mλ/2n_(wg) may beemployed (where m is a non-negative integer diffractive order, andn_(wg) is the effective index of the channel waveguide). An example isshown schematically in FIG. 5A, wherein substantially identical,substantially uniformly spaced diffractive elements 25 are providedalong channel waveguide core 23. Desired spectral profiles of thelocking transfer functions differing from that produced by a simpleperiodic diffractive element set may be achieved by manipulation ofrelative amplitude or phase (i.e. apodization) of portions of theoptical signal diffracted by each element of the locking diffractiveelement sets, in turn achieved by proper relative arrangement of thediffractive elements in the planar waveguide. An example is shown inFIG. 5B, wherein the transverse extent of the diffractive elements 31varies (introducing amplitude variation), and the spacing of thediffractive elements along channel waveguide core 29 varies as well(introducing phase variation, as at 30). This is described inhereinabove or disclosed in the references incorporated hereinabove.While the strongest diffraction of the optical signal occurs for afirst-order set of diffractive elements (i.e. m=1), any diffractiveorder may be employed for providing the locking feedback optical signal.The overall reflectivity of the locking diffractive element sets may beselected to yield desired laser performance (within operationallyacceptable limits), and may typically range between about 1% and about50%. The appropriate choice of locking reflectivity depends on severalvariables, including laser drive current, laser power, laser cavityround-trip optical gain or loss, optical losses or spurious reflectivitybetween the laser and the channel waveguide, and so on.

The locking diffractive element sets may be positioned in the planarwaveguide 1001 so that the optical round trip time between the backreflector of the laser and the distal end of the corresponding lockingdiffractive element set is less than the bit modulation period to beemployed when using the lasers as data transmitters. For example, if themaximum desired data transmission rate is 2.5 Gbit/sec and the averageeffective index within the combined laser and channel waveguide cavityis about 1.5, then the total length (from back laser reflector to distalend of locking diffractive element set) should be less than about 4 cm,typically between a few millimeters and about 2 cm. The reflectivebandwidth of the locking diffractive element set may be chosen to be onthe order of the longitudinal mode spacing of the combined laser andchannel waveguide cavity; smaller reflective bandwidth may result inunacceptably large laser power fluctuations as the cavity modes shiftrelative to the reflective bandwidth. The reflective bandwidth should besufficiently wide to support a desired laser modulation rate ormodulation bandwidth. Reflectivity of the interface between the lasers1015 and the proximal ends of the channel waveguides may be chosen toyield desired laser performance. For example, it may be desirable toprovide an anti-reflection coating (a single λ/4 layer, a λ/4 stack, orother) between the laser and the proximal end of the channel waveguide(on a laser facet, or on the proximal end face of the channelwaveguide). Alternatively, it may be desirable to provide enhancedreflectivity between the laser and the channel waveguide. It may bedesirable to manipulate the launch conditions between the lasers 1015and the proximal ends of the corresponding channel waveguide cores 1003.For example, spatial mode matching may result in less optical loss, agreater fraction of the laser power being launched into the channelwaveguide, and a higher level of locking feedback optical signal gettingback to the laser. This may be achieved (within operationally acceptablelimits) by suitable configuration, adaptation, or arrangement of thelaser or the proximal end of the channel waveguide core 1003, or byadditional optical components employed between the laser and channelwaveguide, such as gradient or refractive lenses.

The fractions of the laser optical signals that are transmitted throughthe corresponding locking diffractive element sets constitute theoutputs of the lasers. The transmitted fractions propagate along thecorresponding channel waveguide cores 1003, exit the correspondingdistal ends thereof, and enter a slab optical waveguide region 1002 ofthe planar waveguide 1001 (FIGS. 1-3). In this region the transmittedfractions of the laser optical signals each propagate in two dimensionsand impinge on routing diffractive element sets 1027, which serve (alongwith distal portions of channel waveguide cores 1003, and channelwaveguide core 1007) as means for routing the transmitted fractions ofthe laser optical signals between the corresponding laser and acorresponding output port. The transmitted fractions of the laseroptical signals are successively incident on the diffractive elements ofthe routing diffractive element sets 1027. The multiple routing sets ofdiffractive elements are each arranged to route at least a portion ofthe transmitted fraction of the corresponding laser optical signal to acorresponding output optical port. In the exemplary embodiments of FIGS.1-3, the distal ends of the channel waveguide cores 1003 function as thecorresponding input ports of the corresponding diffractive element sets1027. All of the routing diffractive element sets may route thecorresponding optical signals to a single output port, or the routedoptical signals may be routed among multiple output optical ports in anydesired combination. An output optical port may comprise the end of achannel waveguide core 1007 formed on the planar waveguide 1001 (FIGS. 1and 2), or may comprise a spatial beam size, beam shape, beam position,and beam propagation direction at an edge of the planar waveguide 1001(designated 1008 in FIG. 3). The routed portions of the correspondinglaser optical signals may enter an optical fiber 1023 positioned at theoutput port 1008 or at the end of channel waveguide core 1007, as thecase may be. The output port(s) may be located on the same edge of theplanar waveguide 1001 as the lasers 1015 (FIG. 1), may be located on anadjacent edge of planar waveguide 1001 (FIGS. 2 and 3), or may belocated in any other suitable location on an edge of planar waveguide1001. If multiple routed portions of the laser optical signals arerouted to a common optical output port, then the corresponding routingdiffractive element sets function as a multiplexer, and enable injectionof multiple wavelength channels into a common optical fiber output.

The multiple routing diffractive element sets 1027 may comprise sets ofcurvilinear diffractive elements, with shapes chosen to route at least aportion of a diverging transmitted fraction of the corresponding laseroptical signal to a corresponding output port, within operationallyacceptable limits. The selection of suitable diffractive element shapesis described hereinabove or disclosed in the references incorporatedhereinabove. The distal end of the channel waveguide cores 1003 may betapered (FIG. 6A) or flared (FIG. 6B), as desired, to yield desireddivergence of the laser optical signals in the slab waveguide region1002. The end of a channel waveguide core 1007, if present, may betapered or flared, as desired, to accommodate convergence of the routedlaser optical signals in the slab waveguide region 1002. Within eachrouting diffractive element set, the diffractive elements may bearranged to yield substantially uniform phase shifts and substantiallysimilar diffracted amplitudes, or may be arranged to yield various phaseshifts and amplitudes to in turn yield a desired routing transferfunction (i.e. desired apodization). The routing transfer function willtypically overlap spectrally the corresponding locking transfer functionimparted by the corresponding locking diffractive element set. Thespacings or other arrangements of the routing diffractive elements areanalogous to those already described for the locking diffractive elementsets, and are described hereinabove or disclosed in the referencesincorporated hereinabove. The multiple routing diffractive element setsmay be longitudinally displaced relative to one another (i.e. “stacked”)and therefore occupy separate areal portions of the slab waveguideregion 1002 of the planar waveguide 1001. Or, the multiple routingdiffractive element sets may occupy overlapping areal portions of theslab waveguide region 1002 of planar waveguide 1001. Such overlappingsets of diffractive elements may be overlaid or interleaved as disclosedin the references incorporated hereinabove.

It is typically intended that the fraction of the laser optical signaltransmitted by the corresponding locking diffractive element set isdiffracted only by the corresponding routing diffractive element set(and a portion thereof thereby routed to the corresponding output port).In this way multiple laser optical signals at multiple corresponding,differing wavelengths from multiple corresponding lasers may be routedto the corresponding output ports, or to a single output port, bydiffraction from the corresponding routing diffractive element sets,even if the optical signals must propagate through other routingdiffractive element sets.

An exemplary use of a multiple-wavelength optical source, such as theexemplary embodiments of FIGS. 1-3, may be transmission of multiplewavelength-differentiated data channels into a single output port orinto a single output optical fiber. Another exemplary use is switchingof a single data channel among multiple carrier wavelengths, byelectronic switching of an electronic modulation signal among thevarious lasers of the multiple-wavelength source. These uses or otheruses of the multiple-wavelength optical sources shall fall within thescope of the present disclosure or appended claims.

Since the locking diffractive element sets and the corresponding routingdiffractive element sets are all formed on the same planar opticalwaveguide, it may be possible to form them in a single lithographic stepor sequence. For example, all of the locking and routing diffractiveelements may be defined on a common mask used to form the diffractiveelements on the planar waveguide. The spectral characteristics of eachlocking diffractive element set and its corresponding routingdiffractive element set, as well as the relative wavelength offsets ofthe various locking diffractive element sets (e.g. to match acorresponding wavelength channel spacing of a WDM system), may be veryprecisely set during the fabrication of such a mask. Once formed, anyshifting of spectral characteristics of the various diffractive elementsets due to environmental influences (such as temperature-inducedwavelength shifts due to thermo-optic effects or thermal expansion ofthe planar waveguide) are well-correlated with one another, since allare formed on a common planar waveguide. If precise control of theabsolute wavelengths is desired, a single temperature control mechanismmay be employed for temperature stabilizing the planar waveguide, andall the diffractive element sets thereon. Such temperature control maybe achieved by any suitable means, including any suitable temperaturesensor, heat source, or feedback circuit, or other mechanism. Themultiple-wavelength optical source may then be temperature-tuned to thedesired wavelengths, or may be stabilized at a desired temperature oroperating wavelengths.

In the exemplary embodiment of FIG. 7, each locking diffractive elementset 1011 includes at least a section of higher-order diffractiveelements 1051 (not visible in FIG. 7; shown in the schematiccross-section of FIG. 8), for redirecting a portion of the correspondinglaser optical signal out of the planar waveguide. While the redirectedportion of the optical signal represents optical loss during propagationalong the channel waveguide, this redirected signal portion may beuseful for monitoring the optical power level propagating along thechannel waveguide. Photodetectors 1047 may be positioned above thehigher-order section of diffractive elements 1051 for receiving theredirected portion of the optical signal. While any higher-orderdiffractive element set (i.e., higher than first order) will redirect aportion of the optical signal out of the planar waveguide, even-orderdiffractive element sets redirect at least one portion vertically fromthe planar waveguide, which may then be more efficiently collected bythe photodetector. In the exemplary embodiment of FIG. 8, most of thelocking diffractive element set 1011 is first-order (element spacing ofλ/2n_(wg)), and the higher-order section 1051 is second-order (elementspacing of λ/n_(wg)).

Photodetectors 1047 may be assembled individually onto the planarwaveguide 1001 over the corresponding higher-order sections 1051 of thediffractive element sets 1011, or the photodetectors may comprise anintegrated photodetector array assembled onto the planar waveguide 1001.Alternatively, photodetectors 1047 may be integrated directly into theplanar waveguide 1001, above or below the higher-order section ofdiffractive elements. The signals generated by the photodetectors 1047may be used to measure the optical signal power propagating through thechannel waveguides for monitoring, diagnostics, trimming, signalnormalization, feedback control, or for other purposes. For example, theplanar waveguide may further comprise multiple corresponding variableoptical attenuators 1043 for controlling the optical power levelpropagating through the segments of the corresponding channel waveguidesdistal to the attenuators. The attenuators 1043 may be operativelycoupled to the corresponding photodetectors 1047 through a feedbackcircuit for maintaining the laser optical signal level reaching thecorresponding routing diffractive element sets 1027 within a selectedoperating range. Alternatively, the signals generated by thephotodetectors 1047 may be used as a feedback signal for controlling thelaser drive current to the corresponding lasers 1015. These and anyother suitable feedback mechanisms shall fall within the scope of thepresent disclosure or appended claims. Higher-order diffractive elements(for redirecting portions of the laser optical signals) orphotodetectors may be positioned elsewhere besides the lockingdiffractive element sets. For example, the routing diffractive elementsets may include higher-order sections, or other portions of channelwaveguide cores 1003 or 1007 (instead of segments thereof having thelocking diffractive element sets) may be provided with a higher-orderset of diffractive elements for redirecting portions of the laseroptical signals onto photodetectors. Any suitable location forpositioning higher-order diffractive elements for redirecting portionsof the laser optical signals to corresponding photodetectors shall fallwithin the scope of the present disclosure or appended claims.

In the exemplary embodiment illustrated schematically in FIG. 9, thelocking diffractive element sets 1011 comprise curvilinear diffractiveelements formed in the slab optical waveguide region 1002. The laseroptical signals emerge from the distal ends of channel waveguide cores1003, propagate in two dimensions through slab waveguide region 1002,and are successively incident on the locking diffractive elements of thecorresponding sets 1011. The schematic cross-sectional views of FIGS.4A-4D may represent curvilinear locking diffractive elements sets 1011.The curvilinear diffractive elements are shaped to redirect a fractionof the laser optical signal back to the laser with a locking transferfunction, in a manner analogous to that described hereinabove forlocking diffractive element sets formed in channel waveguides. Suitablecurvilinear shapes may be determined in a manner analogous to those usedfor determining the curvilinear shapes of the routing diffractiveelement sets, as described hereinabove or disclosed in the referencesincorporated hereinabove. The fractions of the corresponding laseroptical signals transmitted by the corresponding locking diffractiveelement sets are successively incident on the elements of thecorresponding routing diffractive element sets 1027, which routeportions of the corresponding laser optical signals to correspondingoutput port(s). The channel waveguide cores 1003 may be omittedcompletely, with the lasers 1015 launching the corresponding laseroptical signals directly into slab waveguide region 1002. Thecurvilinear locking diffractive elements sets may include higher-ordersections thereof, for directing a portion of the corresponding laseroptical signals out of the planar waveguide, and correspondingphotodetectors may be positioned for receiving these correspondingredirected portions. The curvilinear locking diffractive element setsmay be stacked, overlaid, or interleaved in a manner analogous to thatdescribed hereinabove for the routing diffractive element set, ordisclosed in the references incorporated hereinabove.

In the exemplary embodiment of FIG. 10, the routing means for routingthe laser optical signals from the corresponding lasers 1015 to thecorresponding output port (channel waveguide 1009 in this example)comprises an arrayed-waveguide grating 1029 formed on planar waveguide1001 (along with distal portions of channel waveguide cores 1003, andchannel waveguide core 1009). Locking diffractive element sets 1011formed along corresponding channel waveguide cores 1003 providecorresponding locking feedback signals to the corresponding lasers 1015.The arrayed-waveguide grating (AWG; also referred to as a phased arrayor phased waveguide array) may be implemented in a variety of ways knownin the art, so that the fractions of the corresponding laser opticalsignals transmitted by the corresponding locking diffractive elementsets 1011 and propagating along corresponding channel waveguide cores1003 are routed to corresponding output port(s). Various other aspectsof the multiple-wavelength optical source may be modified as alreadydescribed herein: lasers 1015 may comprise individual lasers assembledwith the planar waveguide, an integrated array of lasers assembled withthe planar waveguide, or lasers integrated into the planar waveguide;locking diffractive element sets 1011 may include correspondinghigher-order sections for redirecting portions of the correspondinglaser optical signals out of the planar waveguide 1001; other portionsof channel waveguide cores 1003, waveguide core 1009, or the AWG 1029may include corresponding higher-order sections for redirecting portionsof the corresponding laser optical signals out of the planar waveguide1001; corresponding photodetectors may receive redirected portions ofthe corresponding optical signals; photodetectors may compriseindividual photodetectors assembled with the planar waveguide, anintegrated array of photodetectors assembled with the planar waveguide,or photodetectors integrated into the planar waveguide; photodetectorsignals may provide feedback control of laser optical signal power; themultiple laser optical signals may be directed to one or more outputoptical ports; or laser optical signals directed to output ports mayenter corresponding optical fibers.

A wide variety of materials may be employed for forming the planarwaveguide and the locking diffractive element sets, channel waveguides,slab waveguide, routing diffractive element sets, arrayed-waveguidegratings, or other elements of a multiple-wavelength optical source, andany suitable material or combination of materials shall fall within thescope of the present disclosure or appended claims. A common materialcombination is a silicon substrate with silica cladding (doped orundoped as appropriate) and with doped silica or silicon nitride orsilicon oxynitride waveguide cores. If lasers or photodetectors are tobe integrated into the planar waveguide, suitable materials must bechosen for the planar waveguide that are compatible with laser orphotodetector materials at the operating wavelengths of the device. Fortypical telecommunications wavelengths, these will typically includeIII-V semiconductors or various alloys thereof.

Whether integrated into the planar waveguide, or assembled with theplanar waveguide as an integrated array, lasers or photodetectors aresubject to yield limitations in their manufacture. So that a singlesub-standard laser or photodetector does not result in rejection of anentire array, arrays may be constructed with extra lasers orphotodetectors. The planar waveguide may be fabricated with extralocking diffractive element sets and extra routing means to accommodatethese extra lasers or photodetectors. In this way, if a laser orphotodetector of an array is bad, the array may still be used. Thecorresponding electronic channels are simply switched on or offaccordingly, to only use channels having a good laser or a goodphotodetector.

In the present disclosure or appended claims, the conjunction “or” is tobe construed inclusively (e.g., “a dog or a cat” would be interpreted as“a dog, or a cat, or both”; Bryan A. Garner, Elements of Legal Style p.103, 2nd ed. 2002), unless: i) it is explicitly stated otherwise, e.g.,by use of “either-or”, “only one of”, or similar language; or ii) two ormore of the listed alternatives are mutually exclusive within thespecific context, in which case “or” would encompass only thosecombinations involving non-mutually-exclusive alternatives, if any.

It should be noted that many of the embodiments depicted in thisdisclosure are only shown schematically, and that not all the featuresmay be shown in full detail or in proper proportion or location. Certainfeatures or structures may be exaggerated relative to others forclarity. In particular, it should be noted that the numbers ofdiffractive elements in an actual device may typically be larger thanthat shown in the Figures. The numbers of diffractive elements isreduced in the Figures for clarity. It should be further noted that theembodiments shown in the Figures are exemplary only, and should not beconstrued as specifically limiting the scope of the written descriptionor the claims set forth herein. It is intended that equivalents of thedisclosed exemplary embodiments or methods shall fall within the scopeof the present disclosure. It is intended that the disclosed exemplaryembodiments or methods, or equivalents thereof, may be modified whileremaining within the scope of the present disclosure or appended claims.

1. A method for forming an optical apparatus, comprising: forming aplanar optical waveguide substantially confining in at least onetransverse spatial dimension optical signals propagating therein;forming at least one set of locking diffractive elements in or on theplanar optical waveguide; forming means for routing an optical signalcorresponding to at least one said set of locking diffractive elements;and positioning a laser corresponding to at least one said set oflocking diffractive elements so as to launch a corresponding laseroptical signal into the planar optical waveguide so that thecorresponding laser optical signal is successively incident on thediffractive elements of the corresponding locking diffractive elementset, wherein: each locking diffractive element set routes within theplanar optical waveguide a fraction of the corresponding laser opticalsignal back to the corresponding laser, with a corresponding lockingtransfer function, as a corresponding locking optical feedback signal,thereby substantially restricting the corresponding laser optical signalto a corresponding laser operating wavelength range determined at leastin part by the corresponding locking transfer function of thecorresponding locking diffractive element set; and each correspondingrouting means routes within the planar optical waveguide, between thecorresponding laser and a corresponding output optical port with acorresponding routing transfer function, at least a portion of thatfraction of the corresponding laser optical signal that is transmittedby the corresponding locking diffractive element set.
 2. The method ofclaim 1, further comprising forming multiple sets of locking diffractiveelement sets and multiple corresponding routing means, and positioningmultiple corresponding lasers so as to launch corresponding laseroptical signals into the planar optical waveguide so that thecorresponding laser optical signals are successively incident on thediffractive elements of the corresponding locking diffractive elementsets.
 3. The method of claim 2, wherein the multiple lasers comprise aset of individual lasers each assembled with the planar opticalwaveguide.
 4. The method of claim 2, wherein the multiple laserscomprise an integrated laser array assembled with the planar opticalwaveguide.
 5. The method of claim 2, wherein the multiple lasers areintegrated into the planar optical waveguide.
 6. The method of claim 5,wherein the planar optical waveguide and the multiple lasers integratedtherein comprise semiconductor materials.
 7. The method of claim 2,further comprising positioning multiple corresponding monitorphotodetectors for receiving portions of the corresponding laser opticalsignals that propagate out of the planar optical waveguide.
 8. Themethod of claim 7, wherein each locking diffractive element setcomprises a corresponding higher-order set of diffractive elements forredirecting a portion of the corresponding laser optical signal topropagate out of the planar optical waveguide and impinge on thecorresponding monitor photodetector.
 9. The method of claim 7, whereineach routing means comprises a corresponding higher-order set ofdiffractive elements for redirecting a portion of the correspondinglaser optical signal to propagate out of the planar optical waveguideand impinge on the corresponding monitor photodetector.
 10. The methodof claim 7, further comprising operatively coupling multiplecorresponding feedback mechanisms to the corresponding monitorphotodetectors for controlling power of the corresponding laser opticalsignals transmitted by the corresponding locking diffractive elementsets.
 11. The method of claim 2, further comprising forming multiplecorresponding channel optical waveguides in the planar optical waveguideand positioning said corresponding channel waveguides for receiving thecorresponding laser optical signals launched from the correspondinglasers into the planar optical waveguide, wherein the correspondinglocking diffractive element sets route within the corresponding channeloptical waveguides the corresponding fractions of the correspondinglaser optical signals back to the corresponding lasers.
 12. The methodof claim 11, further comprising forming the corresponding channeloptical waveguides with tapered or flared end segments for delivering tothe corresponding routing means the portions of the corresponding laseroptical signals transmitted by the corresponding locking diffractiveelement sets.
 13. The method of claim 2, further comprising forming aslab waveguide region in the planar optical waveguide and positioningsaid slab waveguide region for receiving the corresponding laser opticalsignals launched from the corresponding lasers into the planar opticalwaveguide, wherein the corresponding locking diffractive element setsroute within the slab waveguide region the corresponding fractions ofthe corresponding laser optical signals back to the correspondinglasers.
 14. The method of claim 13, further comprising overlaying thecorresponding locking diffractive element sets.
 15. The method of claim13, further comprising displacing longitudinally the correspondinglocking diffractive element sets relative to one another.
 16. The methodof claim 13, further comprising interleaving the corresponding lockingdiffractive element sets.
 17. The method of claim 13, further comprisingforming the diffractive elements of the multiple locking diffractivesets so as to comprise curvilinear diffractive elements.
 18. The methodof claim 2, wherein the corresponding laser operating wavelength rangessubstantially correspond to operating wavelength channels of a WDMtelecommunications system.
 19. The method of claim 2, further comprisingforming the planar optical waveguide so as to comprise a core andcladding, and forming the diffractive elements of the multiple lockingdiffractive element sets in the core, in the cladding, on the cladding,or at an interface between the core and the cladding.
 20. The method ofclaim 2, further comprising forming the multiple corresponding routingmeans: so as to comprise multiple corresponding routing diffractiveelement sets formed in a slab optical waveguide region of the planaroptical waveguide; and so that the corresponding fractions of thecorresponding laser optical signals transmitted by the correspondinglocking diffractive element sets are successively incident on thediffractive elements of the corresponding routing diffractive elementsets.
 21. The method of claim 20, further comprising overlaying thecorresponding routing diffractive element sets.
 22. The method of claim20, further comprising displacing longitudinally the correspondingrouting diffractive element sets relative to one another.
 23. The methodof claim 20, further comprising interleaving the corresponding routingdiffractive element sets.
 24. The method of claim 20, further comprisingforming the corresponding routing diffractive element sets so that thecorresponding portions of the multiple corresponding laser opticalsignals transmitted by the corresponding locking diffractive elementsets are routed by the corresponding routing diffractive element sets toa common output optical port.
 25. The method of claim 20, furthercomprising positioning at least one optical fiber for receiving from theplanar optical waveguide the corresponding portions of the multiplecorresponding laser optical signals transmitted by the correspondinglocking diffractive element sets and routed by the corresponding routingdiffractive element sets to the corresponding output optical ports. 26.The method of claim 20, further comprising forming the diffractiveelements of the multiple routing diffractive sets so as to comprisecurvilinear diffractive elements.
 27. The method of claim 20, furthercomprising forming the planar optical waveguide so as to comprise a coreand cladding, and forming the diffractive elements of the multiplerouting diffractive element sets in the core, in the cladding, on thecladding, or at an interface between the core and the cladding.
 28. Themethod of claim 2, further comprising forming the multiple correspondingrouting means so as to comprise an arrayed waveguide grating in theplanar optical waveguide.
 29. The method of claim 28, further comprisingforming the arrayed waveguide grating so as to route the correspondingportions of the multiple corresponding laser optical signals transmittedby the corresponding locking diffractive element sets to a common outputoptical port.
 30. The method of claim 28, further comprising positioningat least one optical fiber for receiving from the planar opticalwaveguide the corresponding portions of the multiple corresponding laseroptical signals transmitted by the corresponding locking diffractiveelement sets and routed by the arrayed waveguide grating to thecorresponding output optical ports.
 31. The method of claim 2, furthercomprising operatively coupling a temperature controller to the planaroptical waveguide for maintaining the planar optical waveguidesubstantially within an operating temperature range.
 32. A method offorming an optical apparatus, the method comprising: forming an opticalwaveguide; forming at least a first set of diffractive elements in or onthe optical waveguide, wherein each diffractive element of the at leastthe first set is formed to route, as a corresponding optical feedbacksignal and within the optical waveguide, a first fraction of acorresponding optical signal incident thereon, and wherein eachdiffractive element of the at least the first set is further formed totransmit a second fraction of the corresponding optical signal incidentthereon; and forming a second set of diffractive elements, wherein eachdiffractive element of the second set is formed to route, within theoptical waveguide, the corresponding second fraction transmitted by eachdiffractive element of the at least the first set, wherein eachdiffractive element of the at least the first set is further formed toimpart a corresponding first transfer function onto the correspondingoptical feedback signal to substantially restrict the correspondingoptical signal to a corresponding wavelength range determined at leastin part by the corresponding first transfer function.
 33. The method ofclaim 32, further comprising positioning an optical source correspondingto the at least the first set of diffractive elements so as to launchthe corresponding optical signal into the optical waveguide.
 34. Themethod of claim 33 wherein each diffractive element of the second set isformed to route the corresponding second fraction between thecorresponding optical source and a corresponding output optical port,and wherein each diffractive element of the second set is further formedto impart a corresponding second transfer function onto thecorresponding second fraction.
 35. A method of operating an opticalapparatus, the method comprising: receiving an input optical signal inan optical waveguide; routing as an optical feedback signal, within theoptical waveguide and by at least a first set of diffractive elementsformed in or on the optical waveguide, a first fraction of the receivedinput optical signal; imparting, by the at least the first set ofdiffractive elements, a first transfer function onto the opticalfeedback signal to substantially restrict the input optical signal to awavelength range determined at least in part by the first transferfunction; transmitting, by the at least the first set of diffractiveelements, a second fraction of the received optical input signal; androuting, within the optical waveguide and by a second set of diffractiveelements, the transmitted second fraction to an optical port.
 36. Themethod of claim 35, further comprising imparting, by the second set ofdiffractive elements, a second transfer function onto the secondfraction routed to the optical port.
 37. The method of claim 35 whereinsaid receiving the input optical signal includes receiving a pluralityof input optical signals from a corresponding plurality of opticalsources, wherein said routing as the optical feedback signal includesrouting a plurality of optical feedback signals by a correspondingplurality of the at least the first set of diffractive elements, whereinsaid imparting the first transfer function includes imparting, by thecorresponding plurality of the at least the first set of diffractiveelements, a corresponding plurality of first transfer functions onto theplurality of optical feedback signals to substantially restrict theplurality of input optical signals to corresponding wavelength rangesdetermined at least in part by the corresponding plurality of firsttransfer functions.
 38. The method of claim 35 wherein said routing thefirst fraction, by the at least the first set of diffractive elements,includes routing the first fraction within a channel waveguide formedwithin the optical waveguide, and wherein the at least the first set ofdiffractive elements is formed within the channel waveguide.
 39. Anoptical apparatus, comprising: an optical waveguide; at least a firstset of diffractive elements formed in or on the optical waveguide,wherein each diffractive element of the at least the first set isconfigured to route, as a corresponding optical feedback signal andwithin the optical waveguide, a first fraction of a correspondingoptical signal incident thereon, and wherein each diffractive element ofthe at least the first set is further configured to transmit a secondfraction of the corresponding optical signal incident thereon; and asecond set of diffractive elements, wherein each diffractive element ofthe second set is configured to route, within the optical waveguide, thecorresponding second fraction transmitted by each diffractive element ofthe at least the first set, wherein each diffractive element of the atleast the first set is further configured to impart a correspondingfirst transfer function onto the corresponding optical feedback signalto substantially restrict the corresponding optical signal to acorresponding wavelength range determined at least in part by thecorresponding first transfer function.
 40. The apparatus of claim 39wherein the diffractive elements of the at least the first set areformed in a channel waveguide located in a first region of the opticalwaveguide, and wherein the diffractive elements of the second set areformed in a slab waveguide located in a second region of the opticalwaveguide.
 41. The apparatus of claim 39, further comprising at leastone optical source configured to provide the corresponding opticalsignal to the at least the first set of diffractive elements formed inor on the optical waveguide.
 42. The apparatus of claim 39, furthercomprising a plurality of photodetectors each configured to receive thecorresponding second fraction routed by the second set of diffractiveelements.
 43. The apparatus of claim 39 wherein each diffractive elementof the second set is further configured to impart a corresponding secondtransfer function onto the corresponding second fraction.
 44. Anapparatus, comprising: optical waveguide means for receiving an inputoptical signal; at least a first set of diffractive element means forrouting, as an optical feedback signal and within the optical waveguidemeans, a first fraction of the received input optical signal, forimparting a first transfer function onto the optical feedback signal tosubstantially restrict the input optical signal to a wavelength rangedetermined at least in part by the first transfer function, and fortransmitting a second fraction of the received optical input signal; anda second set of diffractive element means for routing, within theoptical waveguide means, the transmitted second fraction to an opticalport.
 45. The apparatus of claim 44 wherein the at least the first setof diffractive element means is formed in a channel waveguide located ina first region of the optical waveguide means, and wherein the secondset of diffractive element means is formed in a slab waveguide locatedin a second region of the optical waveguide means.
 46. The apparatus ofclaim 44, further comprising at least one optical source means forlaunching at least a corresponding portion of the input optical signalinto the optical waveguide means.
 47. The apparatus of claim 44, furthercomprising a plurality of detector means for receiving the secondfraction transmitted to the optical port by the second set ofdiffractive element means.
 48. A system, comprising: a plurality ofoptical sources to respectively provide corresponding input opticalsignals; and an optical waveguide that includes: at least a first set ofdiffractive elements, wherein each diffractive element of the at leastthe first set is configured to route, as a corresponding opticalfeedback signal and within the optical waveguide, a first fraction of acorresponding input optical signal incident thereon, and wherein eachdiffractive element of the at least the first set is further configuredto transmit a second fraction of the corresponding optical signalincident thereon; and a second set of diffractive elements, wherein eachdiffractive element of the second set is configured to route, within theoptical waveguide, the corresponding second fraction transmitted by eachdiffractive element of the at least the first set, wherein eachdiffractive element of the at least the first set is further configuredto impart a corresponding first transfer function onto the correspondingoptical feedback signal to substantially restrict the correspondingoptical signal to a corresponding wavelength range determined at leastin part by the corresponding first transfer function, and wherein eachcorresponding wavelength range substantially corresponds to an operatingwavelength channel.
 49. The system of claim 48 wherein each saidoperating wavelength channel is a channel of a wavelength divisionmultiplexing (WDM) system.
 50. The system of claim 48 wherein theplurality of optical sources includes a plurality of lasers.
 51. Thesystem of claim 49, further comprising a plurality of detectors eachconfigured to receive the corresponding second fraction routed by thesecond set of diffractive elements.